The present invention relates generally to a convenient, simplified, portable, and self-contained instrument for rapid collection, analysis, and measurement of low levels of airborne contaminants found in various environments. More specifically, the present invention is an improvement in field collection and measurement of airborne lead, cadmium, copper and mercury contamination. A field deployable instrument is described which is capable of automated airborne contaminant collection as well as precise, accurate, and automatic measurement of various contaminants in a wide range of in situ sampling environments.
In the field of airborne contamination sampling, heavy metals and undesirable environmental toxins such as lead and mercury tend to be preferentially absorbed onto solid surfaces or absorbed into liquids, notably airborne solid particulates and suspended water droplets. Accurate airborne contaminant concentration levels are monitored through collection and analysis of these particulates and droplets absorbing contaminants and the free suspended contaminants.
Because contaminant samples are typically found in low concentrations within relatively large air volumes, pre-concentration of these collected samples is a necessary practice among sampling and analysis methods. Typically used in air and liquid sampling applications, pre-concentration increases the ability of detection instruments to identify very low contamination levels. Direct liquid absorption is commonly used to concentrate airborne contaminants by dissolving them into a liquid solvent. Subsequent analysis of this contaminant-rich solvent yields the detection or measurement of contaminants extracted from the air.
Handheld electro-monitor devices are known in the art of environmental monitoring and they currently enable their users to field analyze various liquid environmental and biological samples, commonly measuring contaminants in water and blood. These instruments provide portable analysis of fluid samples containing trace contaminants of undesirable toxins such as lead and mercury using electrochemical analysis methods, such as anodic stripping voltammetry. Portability and simplicity are key advantages of such apparatuses for field and lab analysis of liquid samples. These improvements are discussed in detail in U.S. Pat. No. 5,873,990, the entire disclosure of which is herein incorporated by reference.
A portable high-throughput liquid-absorption air sampler (PHTLAAS) capable of collection and direct liquid absorption of airborne contaminants is disclosed in U.S. Pat. No. 6,087,183. The PHTLAAS uses direct liquid absorption to collect and concentrate airborne contaminants into a liquid solvent and then subsequently analyze them to detect and measure dissolved airborne contaminant concentrations. The apparatus uses a fan to blow contaminant rich air through a small diameter tube and into its interior walls, which are wetted with a film of solvent. The fan directs the sample airflow into the liquid film, thereby impinging the airborne contaminants and contacting them with solvent. The contaminants are then dissolved by the solvent, which is preferentially selected for its ability to dissolve the airborne contaminants. The solvent is then collected and analyzed using an instrument to measure contaminant concentration.
While OSHA does not specify a particular method for monitoring respirable lead, it does set a performance standard for any method chosen. These codified standards, the OSHA General Industry Standard for Lead and the Construction Industry Standard for Lead, 29 CFR 1910.1025(d)(9) and 29 CFR 1962.62(d)(9), respectively, provide requirements for the airborne lead analyzer. Compliance with the OSHA General Industry Standard for Lead requires the method for determining airborne lead concentration to have a +/xe2x88x9220% accuracy within 95% confidence limits and result in greater than 80% recovery of the airborne lead for analysis. The standard is a major driving force behind innovation in the field because available technology struggles to meet this standard.
At present, airborne monitoring is a two step process often using two separate instruments to first collect and concentrate samples and then analyze them. The two instrument process creates unnecessary complications and hinders rapid return of test results. Additionally, the minimization of wastes generated from collection and subsequent analysis of potentially dangerous pollutants is not addressed by available technology.
The present invention is directed to both an apparatus and a method for accurate and reliable measurement of airborne contamination yielding a unit contaminant per unit volume sampled air measurement, while at the same time minimizing the generation of hazardous wastes as a by-product of the collection and analysis process.
One object of the present invention is to provide a singular, self-contained instrument for automatic airborne contaminant collection, concentration, measurement, and near real-time analysis within a self-contained instrument.
In the preferred embodiment, the collection system comprises an air pump for drawing sample air through an inlet tube, filter, and a flow meter. The air filter is a membrane filter with a 25 mmxc3x970.8 micron pore size with a capture efficiency of 99.99%. In the preferred embodiment, the high efficiency filter satisfies OSHA requirements for capture efficiency and thereby improves accuracy shortcomings of alternative collection systems.
Additionally, the preferred embodiment permits calculation of contaminant concentration in units of parts per million (ppm) or parts per billion (ppb), which is another object of the invention. The preferred embodiment not only uses an air pump capable of moving high volumes of sample air through the collection system to offer high contaminant capture, but also uses a flow meter to simultaneously measure the airflow volume and returns faster results than available in alternative two step technologies. The preferred embodiment displays the resulting calculated values on an instrument mounted LCD on the face of the unit and also enables the data to be downloaded to a personal computer using an attached RS-232 interface data-port.
Another object of the present invention is to provide an instrument capable of performing analysis on both pre-collected test samples and near real-time samples. To achieve this object, the preferred embodiment features an inlet flange for detachably connecting an inlet tube module. This feature gives the present invention the flexibility to collect contaminant samples for immediate analysis or to analyze previously collected contaminant samples, which were collected by the present invention or by other collection devices. In the preferred embodiment, the apparatus may readily accept personal breathing zone monitors for analysis and measurement of contamination acquired by personnel using the monitors.
In the preferred embodiment, the concentration system is comprised of a user selected analysis media and a system of tubing connecting the inlet air filter, a syringe pump, the scrubbing media, and the measurement and analysis system. Chief among selection criteria for the analysis media is its ability to solubilize proscribed contaminants, but also include among other concerns, cost, disposal concerns, and availability.
To satisfy another objective of the invention, the preferred embodiment uses a metal removal media or device to minimize hazardous waste byproducts and accumulated collected lead particles. To achieve this objective, the preferred embodiment uses a pump, which, may be, for example, syringe pump, to pull contaminant-rich analysis media through an ion-exchange media after analysis of a contaminant sample is complete. The ion-exchange media cartridge binds contaminants dissolved within the analysis media within the cartridge and prevents contaminants from remaining soluble in the analysis media. As a result, waste is minimized and the analysis media can be reused.
In the preferred embodiment, the syringe pump acts as a reservoir for the analysis media, both prior to concentrating contaminants trapped in the air filter and also after scrubbing the contaminant from the analysis media.
In the preferred embodiment, the apparatus uses annodic stripping voltammetry (ASV) to measure solubilized contaminants in the analysis media. However, other methods for measurement of contaminant are contemplated, such as chemilunescence, colorimetrics, as well as other electro-chemical detection devices and not solely ASV devices.
In the preferred embodiment, the apparatus may operate using a source of external alternating current. Additionally, the preferred embodiment has a rechargeable internal battery within the apparatus, giving the apparatus portability for field use.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and will become apparent to those skilled in the art upon examination of the following drawings or may be learned by practicing the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.